Liver-specific Inactivation of the Abetalipoproteinemia Gene Completely Abrogates Very Low Density Lipoprotein/Low Density Lipoprotein Production in a Viable Conditional Knockout Mouse

Chang, Benny Hung-Junn; Liao, Wei; Li, Lan; Nakamuta, Makoto; Mack, David R.; Chan, Lawrence

doi:10.1074/jbc.274.10.6051

Cited by 119 publications

(113 citation statements)

References 26 publications

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“…Comparisons between Pemt Ϫ/Ϫ Mice and Mice That Lack Microsomal TG Transfer Protein-One model system that has a defect in apoB100 secretion similar to that observed in Pemt Ϫ/Ϫ mice is mice in which the microsomal TG transfer protein (MTP) gene was ablated in murine liver (35,36). MTP has been shown to transfer TG and PC between membranes in vitro (37).…”

Section: Discussionmentioning

confidence: 99%

An Unexpected Requirement for PhosphatidylethanolamineN-Methyltransferase in the Secretion of Very Low Density Lipoproteins

Noga¹,

Zhao

Vance

2002

Journal of Biological Chemistry

213

164

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Phosphatidylethanolamine N-methyltransferase (PEMT) catalyzes the conversion of phosphatidylethanolamine to phosphatidylcholine (PC). We investigated whether there was diminished secretion of lipoproteins from hepatocytes derived from mice that lacked PEMT (Pemt ؊/؊ ) compared with Pemt ؉/؉ mice. Hepatocytes were incubated with 0.75 mM oleate, the media were harvested, and triacylglycerol (TG), PC, apolipoprotein (apo) B100, and apoB48 were isolated and quantified. Compared with hepatocytes from Pemt ؉/؉ mice, hepatocytes from Pemt ؊/؊ mice secreted 50% less TG, whereas secretion of PC was unaffected. Fractionation of the secreted lipoproteins on density gradients demonstrated that the decrease in TG was in the very low density lipoprotein (VLDL)/low density lipoprotein fractions. The secretion of apoB100 was decreased by ϳ70% in VLDLs/ low density lipoproteins, whereas there was no significant decrease in apoB48 secretion in any fraction. Transfection of McArdle hepatoma cells (that lack PEMT) with PEMT cDNA enhanced secretion of TG in the VLDLs. Because the levels of PC in the hepatocytes and hepatoma cells were unaffected by the lack of PEMT expression, there appears to be an unexpected requirement for PEMT in the secretion of apoB100-containing VLDLs.

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Section: Discussionmentioning

confidence: 99%

An Unexpected Requirement for PhosphatidylethanolamineN-Methyltransferase in the Secretion of Very Low Density Lipoproteins

Noga¹,

Zhao

Vance

2002

Journal of Biological Chemistry

213

164

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“…6, which is published as supporting information on the PNAS web site, www.pnas.org). We used R1 embryonic stem (ES) cells and generated knockout clones as described (12). Nine positive R1 ES cell clones were injected into C57BL͞6J blastocysts, and chimera mice were crossed to C57BL͞6J mice and germ-line transmission was confirmed in eight.…”

Section: Methodsmentioning

confidence: 99%

“…Mice were weaned at 21 days and fed eithercolumns connected in series (Pharmacia FPLC System, Amersham Pharmacia Biotech). Fractions of 0.5 ml were collected with an elution buffer (1 mM EDTA͞154 mM NaCl͞0.02% NaN 3 , pH 8.2) as described (12): fractions 4-9, very low-density lipoprotein (VLDL); 10-20, intermediate-density lipoprotein (IDL)͞LDL; and 22-32, HDL. Northern blotting and immunoblotting by using the probes and antibodies identified in the figure legends was performed as described (12).…”

Section: Methodsmentioning

confidence: 99%

Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism

Çilingiroğlu

Otvos

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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High-density lipoprotein (HDL) protects against atherosclerosis. Endothelial lipase (EL) has been postulated to be involved in lipoprotein, and possibly HDL, metabolism, yet the evidence has been scarce and conflicting. We have inactivated EL in mice by gene targeting. EL ؊/؊ mice have elevated plasma and HDL cholesterol, and increased apolipoproteins A-I and E. NMR analysis reveals an abundance of large HDL particles. There is down-regulation of the transcripts for phospholipid transfer protein, but up-regulation of those for hepatic lipase and lipoprotein lipase. Plasma lecithin:cholesterol acyltransferase is unchanged despite an increase in hepatic mRNA; lecithin:cholesterol acyltransferase activity toward endogenous EL ؊/؊ substrate is, however, reduced by 50%. HDL clearance is decreased in EL ؊/؊ mice; both the structure of HDL and the presence of EL are factors that determine the rate of clearance. To determine EL's role in humans, we find a significant association between a single-nucleotide polymorphism 584C͞T in the EL (LIPG) gene and HDL cholesterol in a well characterized population of 372 individuals. We conclude that EL is a major determinant of HDL concentration, structure, and metabolism in mice, and a major determinant of HDL concentration in humans.lipoprotein metabolism ͉ atherosclerosis ͉ gene targeting

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“…10 (GTT) at 8, 14, 28, and 42 weeks for male mice (weighing 20 -26 g) and at 8, 14, 26, and 38 weeks for female mice (weighing 18 -22 g). For GTT, we injected intraperitoneally 1.5 g of glucose/kg following a 12-h fast as described (2,11). For ITT, we administered an intraperitoneal injection of regular insulin (1 unit/kg body weight) (Humulin R) to mice after an overnight fast.…”

Section: Methodsmentioning

confidence: 99%

“…Northern Blotting of RNA-We isolated total RNA from snap-frozen tissue samples using TRIzol (Invitrogen) reagent according to the manufacturer's instructions (16), and we performed the Northern blots as described previously (11,17). Briefly, we fractionated the total RNA (20 g/sample) on a 1.2% agarose, 2 M formaldehyde gel and electrotransferred it to a Hybond N1 membrane (Amersham Biosciences).…”

Section: Methodsmentioning

confidence: 99%

Metabolic Adaptations in the Absence of Perilipin

Saha

Kojima

Martı́nez-Botas

et al. 2004

Journal of Biological Chemistry

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101

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Targeted disruption of the lipid droplet protein, perilipin, in mice leads to constitutional lipolysis associated with marked reduction in white adipose tissue as a result of unbridled lipolysis. To investigate the metabolic adaptations in response to the constitutive lipolysis, we studied perilipin-null (plin ؊/؊ ) mice in terms of their fatty acid oxidation and glycerol and glucose metabolism homeostasis by using dynamic biochemical testing and clamp and tracer infusion methods. plin ؊/؊ mice showed increased ␤-oxidation in muscle, liver, and adipose tissue resulting from a coordinated regulation of the enzymes and proteins involved in ␤-oxidation. The increased ␤-oxidation helped remove the extra free fatty acids created by the constitutive lipolysis. An increase in the expression of the transcripts for uncoupling proteins-2 and -3 also accompanied this increase in fatty acid oxidation. Adult plin ؊/؊ mice had normal plasma glucose but a reduced basal hepatic glucose production (46% that of plin ؉/؉ ). Insulin infusion during low dose hyperinsulinemic-euglycemic clamp further lowered the glucose production in plin ؊/؊ mice, but plin ؊/؊ mice also showed a 36% decrease (p < 0.007) in glucose disposal rate during the low dose insulin clamp, indicating peripheral insulin resistance. However, compared with plin ؉/؉ mice, 14-week-old plin ؊/؊ mice showed no significant difference in glucose disposal rate during the high dose hyperinsulinemic clamp, whereas 42-week-old plin ؊/؊ mice displayed significant insulin resistance on high dose hyperinsulinemic clamp. Despite increasing insulin resistance with age, plin ؊/؊ mice at different ages maintained a normal glucose response during an intraperitoneal glucose tolerance curve, being compensated by the increased ␤-oxidation and reduced hepatic glucose production. These experiments uncover the metabolic adaptations associated with the constitutional lipolysis in plin ؊/؊ mice that allowed the mice to continue to exhibit normal glucose tolerance in the presence of peripheral insulin resistance.Obesity is a growing health problem with significant associated morbidity and mortality. Although obesity can result from environmental factors and a sedentary life-style, recent findings suggest that susceptibility to obesity is to a large extent genetically determined (1). One approach to study obesity and its associated morbidity is to investigate genes and pathways involved in the regulation of lipid metabolism and body fat deposition. A fat cell protein, perilipin, has recently been found to play a key role in determining body habitus as its absence leads to a lean and obesity-resistant phenotype in mice (2, 3). Perilipin belongs to a class of proteins found exclusively at the limiting surface of storage droplets in adipocytes and in steroidogenic cells (4 -7). It coats the lipid droplets and protects triglycerides from the lipolytic action of hormone-sensitive lipase (6). Hormone-sensitive lipase catalyzes the breakdown of triacylglycerols and the release of free fatty acids ...

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Liver-specific Inactivation of the Abetalipoproteinemia Gene Completely Abrogates Very Low Density Lipoprotein/Low Density Lipoprotein Production in a Viable Conditional Knockout Mouse

Cited by 119 publications

References 26 publications

An Unexpected Requirement for PhosphatidylethanolamineN-Methyltransferase in the Secretion of Very Low Density Lipoproteins

An Unexpected Requirement for PhosphatidylethanolamineN-Methyltransferase in the Secretion of Very Low Density Lipoproteins

Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism

Metabolic Adaptations in the Absence of Perilipin

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